Papers by Author: Hiroyuki Muto

Abstract: Gold nanorods (GNRs) were deposited in ordered mesoporous silica SBA-15 by a liquid-phase synthesis. The X-ray diffraction pattern of GNRs-deposited SBA-15 (GNRs/SBA-15) confirmed that the mesoporous structure of the SBA-15 was maintained even after depositing GNRs in the SBA-15 pores. Laser irradiation and heat treatment for GNRs/SBA-15 were carried out to check the effect on the GNRs morphology alteration. These treatments were found to shorten the length of the GNRs in SBA-15, leading to a blue shift of the surface plasmon resonance wavelength of the GNRs. Especially, heat treatment at high temperatures, e.g. at 500 °C, showed unique result that the inner wall of SBA-15 was collapsed by the overgrowth of gold nanoparticles.

Abstract: Titanate nanosheet thick films were prepared on indium-tin oxide (ITO)-coated glass substrates by electrophoretic deposition. Three types of sols with different preparation procedures and pH values were prepared. In the case of titanate nanosheet films prepared from a sol with pH=7.0, surface of the films was flat and nanosheets which deposited on substrates were uniformly dense. Titanate nanosheet thick film deposited from the sol using dimethyl ethanol amine for the exfoliation showed a high photocatalytic activity due to the high crystallinity

Abstract: Preparation of monodispersed inorganic-organic hybrid particles has become one of the most attractive research topics in recent years. In this study, phenylsilsesquioxane (PhSiO3/2) particles were synthesized from phenyltriethoxysilane (PhSi(OEt)3), ethanol (EtOH), hydrochloric acid for hydrolysis and ammonia water for polycondensation by the sol-gel method. Spherical PhSiO3/2 particles were obtainable by varying the mole ratios of EtOH, H2O, HCl and NH3, to PhSi(OEt)3. The particle size was changed from 0.1 to 5.0 .m with the mole ratio. Under the optimum conditions, monodispersed particles with 1.50 .m in diameter and 0.05 of normalized standard deviation were successfully prepared.

Abstract: Anatase nanocrystals were formed on sol-gel derived SiO2-TiO2 coatings with water vapor or hot water treatments. The anatase nanocrystals were precipitated through hydrolysis of Si-O-Ti bonds, dissolution of SiO2 component, migration of hydrolyzed titania species, and nucleation and growth. The process temperatures can be lowered below 60oC, which should open new applications. It was found that the crystal habit of titania was changes from roundish anatase to sheet-like titania by applying vibration during the hot water treatment. The nanosheets were identified as hydrated titania, TiO2 . mH2O, with layerd structure. The coatings of hydrated titania showed high photocatalytic activities and excellent antifogging properties due to their unique morphology.

Abstract: The contact deformation mechanisms of a superplastic ceramic, 3Y-TZP (3mol % yttria-partially stabilized tetragonal zirconia polycrystals) are examined in indentation creep tests at high temperatures. A large discrepancy between the uniaxial compression and the pyramidal indentation contact behaviors is observed. The indentation creep curves exhibit a hardening behavior, i.e., the penetration rate decreases as the penetration depth and/or the creep time increases. This fact implied that the cooperative grain-boundary sliding (CGBS) in a microscopically localized region, such as the sub-surface contact region beneath a pyramidal indenter, is very limited through the microscopic processes of localized grain interlocking.

Abstract: Methylsilsesquioxane films were formed on glass substrates by dropping a sol prepared from methyltriethoxysilane and then heat-treated in an oven. Nanoindentation test was performed to assess the elastoplastic properties of the films, including the relative residual depth ξr, Meyer hardness HM, work-of-indentation WI and the elastic modulus E’. The values of ξr, HM and WI were obtained by a Berkovich indenter and E’ was determined by a spherical indenter on the basis of Hertz elastic theory. ξr decreased with the increase in the heat treatment time, whereas HM , WI and E’ significantly increased with the time. The changes in the mechanical properties with the heat treatment time well reflected the evolution of the Si-O-Si network structure in methylsilsequioxane film.

Abstract: In order to fabricate an alumina ceramics with high density at low sintering temperature, nanosized γ–Al2O3 powders with average size of 9.7 nm were added to microsized γ–Al2O3 powders with 2 #m and they were well mixed. Its sintering behavior was studied in the temperature range of 1000oC to 1300oC and in holding time from 1 hour to 10 hours. Compacted samples with a different mixed ratio of nanosized and microsized Al2O3 powders (N/M ratio) were prepared and pressured at 1 GPa in a uniaxial direction. The phase transformation from γ–Al2O3 to α–Al2O3 takes place at 1100oC for 1hour sintering in all compacted samples. This rate is increased with increasing N/M ratio. The relative density varied from 70% to 95% depending on temperature and N/M ratio. With increasing sintering temperature from 1000oC to 1300oC, it was changed from 70% to 93%. Especially, the relative density was enhanced about 9% higher than that of only microsized sample by only 10 wt% addition of nanosized powders.

Abstract: A novel indentation method is proposed to study the mechanical properties of porous and/or heterogeneous materials by the use of a cylindrical indenter with line loading on test specimens. The problems in line contact are examined. The indentation load P versus penetration depth h relation in line contact is expressed in terms of the radius R of cylindrical indenter and the contact length L. An application of a cylindrical indentation to a polycrystalline graphite leads to a successful determination of the Young's modulus and the yielding strength. It is concluded that the line contact rather than the conventional pyramidal point contact is more efficient for the experimental deternination of mechanical properties of porous and/or heterogeneous materials.